"...if decentralisation is what makes Bitcoin good, and growth threatens decentralisation, then Bitcoin should not be allowed to grow.
Honestly it's hard to disagree with this statement. Growing now at a cost of centralization is very short sighted. I do believe that centralization is Bitcoins' Achilles' heel. Now how much centralization would a 2MB or an 8MB block cause that can be debated. Don't really get the end of the world catastrophe just yet. Lets get SegWit in there, and bump blocks to 2MB to be extra conservative, and have a sidechain do 0 confs, then we party!